The proposed research will examine how the limited capacity of working memory constrains the on-line processing in language comprehension. Comprehension performance changes qualitatively and quantitatively when the resource demands of the task exceed the supply. The proposed research experimentally examines I what kinds of task demands exacerbate resource shortages, how resource shortages are accommodated by the, i system, and how individual differences in maximum capacity affect performance. The empirical studies examine working memory constraints on four aspects of language comprehension. One series of experiments investigates the relation between syntactic modularity and working memory capacity, examining the hypothesis that a resource-demanding interaction between syntactic and semantic processing occurs only in those Individuals and tasks in which the required resources are available. A second series examines whether the larger capacity of some individuals permits them to maintain multiple Interpretations of a structurally or lexically ambiguous sentence. A third series investigates how the storage of information over a text distance varies with the processing demands made by the intervening text. A fourth series develops the methodology of pupillometry to index the consumption of cognitive resources during language comprehension. In addition, the experimental methodologies include the measurement of gaze locations and durations during reading, measurement of word-by-word self- paced reading times, and cross-modal priming. The methodologies are used to answer questions about the time course, content, and intensity of processing. The theory will be instantiated as a computational model, namely an activation-based production system , in which both processing and storage are fueled by activation. In this model, the total amount of activation, available to the system has an upperbound that corresponds to the maximum capacity of an individual. The goal of the theory is to explain how the processing of language accommodates (or fails to accommodate) tile transient computational and storage demands that occur in language comprehension, and to thereby explain the variation in comprehension among tasks and individuals. One health-related implication of this research is that the theory will explain a dimension of individual differences that potentially encompasses not just normal variation in comprehension, but also variation due to extreme age, to stress, or to trauma. Second, the research develops new methodologies with clinical potential (relating eye fixations to cognitive processes and relating pupil dilation to the consumption of cognitive resources). Third, the research develops the theoretical analysis of a psychometric instrument (the reading span test) that may prove useful for measuring age and disease-related changes in language functioning.